tDCS-induced alterations in GABA concentration within primary motor cortex predict motor learning and motor memory: a 7 T magnetic resonance spectroscopy study.
Bottom Line: Note that adaptation to a robot-induced force field has long been considered to be a form of model-based learning that is closely associated with the computation and 'supervised' learning of internal 'forward' models within the cerebellum.This effect was specific to GABA, localised to the left motor cortex, and was polarity specific insofar as it was not observed following either cathodal or sham stimulation.Importantly, we show that the magnitude of tDCS-induced alterations in GABA concentration within motor cortex predicts individual differences in both motor learning and motor memory on the robotic force adaptation and de-adaptation task.
Affiliation: Brain and Body Centre, School of Psychology, University of Nottingham, UK.Show MeSH
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Mentions: In the MR spectroscopy session, each group received either anodal, cathodal, or sham stimulation. Correlation analyses using Pearson's r were conducted to examine the relationship between tDCS-induced plasticity – measured by the change in GABA concentration change ratios induced by anodal, cathodal, or sham stimulation, and motor learning – measured by the reaching errors recorded during the adaptation and de-adaptation phases of the force adaptation task. These analyses revealed that there was a statistically significant correlation between individual motor learning performance in both the adaptation and the de-adaptation phases of the force adaptation task and GABA concentration change ratios measured within the left M1 VOI following anodal tDCS. These data are presented in Figs. 3c and d. The magnitude of the decrease in MRS-GABA in left M1 induced by anodal tDCS was positively associated with the magnitude of error during the adaptation phase (Pearson's r = 0.78, p < 0.05) and the de-adaptation phase (Pearson's r = 0.68, p < 0.05) of the force adaptation task. Participants who showed large decreases in GABA after anodal tDCS performed better (i.e., exhibited smaller errors during the adaptation phase) and increased motor memory retention (i.e., larger errors in the de-adaptation phase) of the force adaptation task. It should be noted however that, for the group receiving anodal tDCS only, force adaptation and de-adaptation performance were correlated with one another. A partial correlation analyses further revealed that while force de-adaptation performance remained strongly positively associated with GABA change ratios (r = 0.61) once force adaptation scores had been accounted for, this effect no longer reached conventional levels of statistical significance (p > 0.1).
Affiliation: Brain and Body Centre, School of Psychology, University of Nottingham, UK.